Some "hammerless" firearms do in fact have hidden hammers, which are located in the action housing. Truly hammerless guns. such as the Savage M99, have a firing mechanism that is based on a spring-activated firing pin.

A hammerless firearm is a firearm that lacks an exposed hammer or hammer spur. One of the disadvantages of an exposed hammer spur is the tendency to get caught on items such as clothing; covering or bobbing the hammer by removing the spur avoids this tendency.